In the traveling-wire electroerosion process, a continuous electrode wire is axially transported by a wire axial drive means from a supply means to a takeup means. In the path of wire travel, a pair of machining guide members may be disposed at opposite sides of an electrically conductive workpiece to stretch or span the traveling electrode wire linearly thereacross to traverse the workpiece, thus positioning the electrode wire in a precise machining relationship with the workpiece. An electrical machining current, typically or preferably in the form of a succession of time-spaced electrical pulses, is applied between the traveling electrode wire and the workpiece across a machining gap flooded with a machining liquid, e.g. an aqueous liquid of dielectric nature or low conductivity, or an aqueous solution of electrolyte, to electroerosively remove material from the workpiece. As the material removal proceeds, the workpiece is displaced transversely to the longitudinal axis or the straight line path of the traveling wire electrode along a prescribed two-dimensional machining feed path under the command, advantageously, of a numerical controller, so that a desired contour of machining is generated in the workpiece.
It is important that the wire electrode be of good conductivity and composed to afford a satisfactory rate of material removal and to be subject to minimal erosive wear. It is desirable that the wire electrode be heat-resistant and retain sufficient tensile strength at a high temperature created by the passage of a machining current of high amperage or current density, and be thus free from breakage in operation. Customarily, the wire electrode is constituted as a single wire having a diameter of 0.05 to 0.5 mm and composed of copper metal or a copper alloy such as brass. Such a wire has been provided by drawing through a die and naturally has had a circular cross section and a smooth peripheral surface.
The machining liquid is supplied, typically from one or more nozzles, into the machining gap to serve on one hand as a gap medium to carry the discharge and/or electrolytic current and on the other hand as a coolant to dissipate heat developed by the passage of the machining current of high amperage or current density required. Higher amperage or current density is desirable to achieve greater removal rate and efficiency, and necessitates renewal of the machining liquid in the gap at a higher rate.
It has, however, been found that the continued supply of the machining liquid in an ample amount towards the machining gap often causes wire breakage and does not allow the use of a greater machining current. When the electrode wire is excessively heated or insufficiently cooled, it tends to break. There is thus a limitation in the heat-dissipation ability of the conventional electrode wire having a smooth and round peripheral surface along its length traversing the machining gap. With the conventional electrode wire having a smooth machining surface, it has also be observed that gases produced by discharges and/or electrolytic decomposition of the delivered machining liquid tend to be adherent on the electrode surface and separate the latter from the coolant liquid and thus to act as a thermal insulator therebetween, and further to allow gaseous discharges essentially of thermal natural to develope thereacross.